Hopper type reactors

The principle of the moving bed of Fig. 3.37a in cross-flow to the air supply is used for roasting zinc blende and for the combustion of large coal on chain grate stokers. Another kind of moving bed is found in hopper-type reactors in which particles are fed at the top and continuously move downwards to be discharged at... 

In the cross-flow conveyor-type reactors (Figure 4.5), the solid particles are fed continuously from a hopper on to a conveyor belt and a gas is passed in the cross-flow direction. This type of reactor is used for the oxidation of metallic ores in metallurgical industries. 

Scale-up of CFBs is generally less of a problem than with bubbling beds [111], Moreover, the higher velocity in CFB means higher gas throughput, which can minimize the reactor costs. Several CFB loop designs have been proposed for getting smooth steady state circulation of solids. Basically, there are two basic types of solids circulation loops distinct in that some include a reservoir of solids while others do not. The solids circulation loops which do not include a reservoir of solids (hopper) are less flexible in operation compared to the circulation systems with reserviors. 

A bank of four horizontal stirred beds is used, one above another, of the screw conveyor type. The top one is for calcination in air to remove traces of nitric acid, water and carbonaceous products, the middle two for hydrofluorination and the lower one mainly for partial sintering and den-sification of the product in hydrogen fluoride. Each stirred bed reactor is 20 ft long and 16 in. internal diameter, the lower ones made of inconel and the upper one of stainless-steel. The powder flows from a hopper at the top, via a seal hopper between the calcination and hydrofluorination sections, to another hopper and feeding system at the bottom, as shown in Fig. 5.8. Air and anhydrous hydrogen fluoride pass in counter-current flow to the solids in the appropriate reactors, the efBuent gases being conducted to suitable filters and dust collectors. 

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